Curl may be induced into sheets of paper due to various handling factors and this may impair the further handling of the sheets. One way in which curl unintentionally is induced in sheets is in the process of transfer and fixing of an image to a sheet in a photocopier. This can particularly be a problem in a duplex copier where the sheet is to be conveyed to a duplex buffer tray from which it is re-fed to the photoreceptor to receive an image on its other side. It may also be a problem where the sheet requires a further processing such as binding in a finisher.
It is often necessary to remove curl from a material in order to process in the material more easily. For example, devices that transport sheets of media (such as copiers, printers, multifunction machines, etc.) often benefit from very flat, de-curled sheets, which reduce the occurrence of jamming and other malfunctions. Similarly, when ribbons or webs of material are unwound from rolls, they may contain a certain amount of curl that needs to be removed.
Various sheet curl control apparatus have been devised. For example, one arrangement of a decurler comprises a pair of co-acting rollers—that is, a feeding roller and an indenting shaft—that form a nip therebetween (note that sometimes rollers are referred to as rolls). One of the rollers is more elastic (softer) than the other roller. Pressure is applied between the rollers to form what is referred to as a “nip” and the material to be curled or de-curled is fed through the nip to have the curl removed or added.
When print media, such as ink, is deposited as a print image on a substrate, such as a sheet of paper, down-curl can be induced on the printed sheet by the image. In particular, this is problematic when a solid stripe of ink is printed on the lead-edge of a sheet. During the de-curling process, the indenting shaft can be placed facing the ink and in contact with the sheet. As a result, the indenting shaft is susceptible to ink contamination as ink from the sheet transfers from the sheet to a surface of the indenting shaft. If ink buildup on the indenting shaft persists, it may cause the sheet to wrinkle in the decurler. Additionally, any ink that deposits on the indenting shaft may be re-deposited on other portions of the same sheet, creating an unacceptable “ink offset” print defect, or as artifacts on subsequent sheets. A decurler that overcomes the limitations described above would be a welcome addition to the art.